1. Field of the Invention
The present invention relates to an image sensing apparatus and, more particularly, to a technique of generating an image focused on an arbitrary focal length from output data after photography.
2. Description of the Related Art
Recently, there has been proposed a technique of storing the intensity distribution and traveling direction of light at the time of photography in an image sensing apparatus such as a digital camera, thereby generating an image focused on an arbitrary focal length from output data after storage.
Ren. Ng, et al. (“Light Field Photography with a Hand-Held Plenoptic Camera”, Stanford University Computer Science Tech Report CTSR 2005 February) discloses a method (Light Field Photography) of separating and storing light beams coming from various directions by forming images of light beams having passed through different pupil regions of the imaging optical system on the pixels (photoelectric conversion elements) of an image sensor via a microlens array. In the obtained output data (Light Field Data: to be referred to as LF data hereinafter), light beams coming from different directions are stored in adjacent pixels. By extracting light beams in the same direction from pixels associated with respective microlenses, an image photographed from this direction can be generated from the LF data. Also, the pixel of an image focused on a specific focal length can be generated (reconstructed) after photography by setting an arbitrary focal length and adding outputs from pixels which store light beams having passed through one point on a focal plane at this focal length.
In an image sensing apparatus using the method as disclosed in Ren. Ng, microlenses are designed in accordance with the effective aperture of the imaging optical system so that the pixels of an image sensor which are assigned to the respective lenses of the microlens array cover light beams having passed through all the regions of the exit pupil of the imaging optical system. This image sensing apparatus is premised on that the f-number (focal length/effective aperture) of the imaging optical system and that of each microlens of the microlens array coincide with each other. However, in an image sensing apparatus such as a lens-interchangeable digital single-lens reflex camera, the f-number of the mounted imaging optical system may change. For this reason, when a reconstructed image focused on an arbitrary focal length is generated from LF data obtained by photography using the method as disclosed in Ren. Ng (non-patent literature 1), no preferable reconstructed image may be generated.